The jump probe addressed here, also referred to as the first jump probe below, is designed to be located in the exhaust line in the outflow direction of an exhaust gas emerging from an internal combustion engine downstream from at least one section of a catalytic converter with an oxygen storage capacity.
The catalytic converter has the capacity to store oxygen so that short-term deviations from the ideal air-fuel ratio λ=1 can be buffered. A control system results in that the extreme cases in which no oxygen at all is stored in the catalytic converter or the oxygen storage reservoir is full do not occur. In the control process the voltage measurement signals of the jump probe to be analyzed are used. Typically, the value of λ oscillates during control around the value λ=1. At this point, the jump probe can deliver an adulterated signal due to ageing. By adulterating the signal, faulty operation can occur during control. It is therefore necessary to make available a method for diagnosing the reliability performance of the indicated jump probe in the installed state in the exhaust gas line.
DE 10 2005 016 075 A1 describes a method for diagnosis of the reliability performance of a lambda probe. In this connection, exhaust gas is supplied to the exhaust gas line, intentionally a sudden change is used in the air-fuel ratio from a rich exhaust gas mixture (an exhaust gas mixture with more fuel than can be burned by the air present) to a leaner exhaust gas mixture (an exhaust gas mixture with more air than necessary to burn the fuel which is present) or vice versa. The change in the air-fuel ratio leads to a jump in the voltage which is acting as the measurement signal. DE 10 2005 106 075 A1 describes that a time interval is measured between the detection of such a jump in the signal of a lambda probe located upstream from the catalytic converter and the detection of a jump in the signal of a lambda probe downstream from the catalytic converter. It is assumed here that this time interval is additively composed of the contribution which is dictated by the oxygen storage capacity of the catalytic converter and the contribution which is dictated by the probe properties. The individual contributions can be deduced according to a certain procedure. The contribution dictated by the probe properties is examined according to a threshold value criterion for whether the probe can be classified as performing reliably or not.
DE 198 28 929 A1 describes a method for checking the dynamic behavior of a measurement transducer in the exhaust gas line of an internal combustion engine in which likewise a change in the air-fuel mixture is used: The signal of the measurement transducer during a regeneration phase is monitored and faulty dynamic behavior is diagnosed when the predetermined signal characteristic is absent.
The disadvantage of the method used in the prior art for diagnosing the reliability performance of a downstream catalytic converter lambda probe is that the oxygen storage capacity of the catalytic converter must be taken into account in the evaluation of the signals. But this is mostly itself an unknown, in particular, the oxygen storage capacity of the catalytic converter can have decreased by its poisoning; this causes effects which cannot be distinguished at all or can hardly be distinguished from the effects caused by probe ageing.
Thus the object of the invention is to make available a method for diagnosing the reliability performance of a lambda probe in the initially described arrangement which can be easily carried out and which is still especially reliable.